Method for producing hydrogenated silicon oxycarbide films

ABSTRACT

A method for producing hydrogenated silicon oxycarbide (H:SiOC) films having low dielectric constant. The method comprises using plasma-assisted polymerization to react a cyclic silane compound containing at least one strained silicon bond to produce the films. The resulting films are useful in the formation of semiconductor devices.

FIELD OF THE INVENTION

[0001] This invention is a method for producing hydrogenated siliconoxycarbide (H:SiOC) films having low dielectric constant. The methodcomprises using plasma-assisted polymerization to react a cyclic silanecompound containing at least one strained silicon bond to produce thefilms. The resulting films are useful in the formation of semiconductordevices.

BACKGROUND OF THE INVENTION

[0002] The use of chemical vapor deposition (CVD) to produce SiO₂,SiNC:H or SiC:H or SiC:O:H thin films on semiconductor devices fromsilicon-containing materials such as silane (SiH₄), tetraethylorthosilicate (TEOS), and methyl-containing silanes such astrimethylsilane has been disclosed in the art. Chemical vapor depositionprocesses typically comprise introducing the gaseous silicon-containingmaterial and a non-Si containing reactive gas into a reaction chambercontaining the semiconductor substrate. An energy source such as thermalor plasma induces the reaction between the silicon-containing materialand reactive gas thereby resulting in the deposition of the thin film ofSiO₂, SiNC:H or SiC:H or SiC:O:H on the semiconductor device. Plasmaenhanced chemical vapor deposition (PECVD) is typically carried out atlow temperatures (<500° C.) thereby making PECVD a suitable means forproducing dielectric and passivation films on semiconductor devices.

[0003] With the industry requirement to minimize the electricalresistance-capacitance (RC) delay associated with the circuitinterconnections, new low permittivity dielectrics are required for useas isolation materials between adjacent conductors. While many candidatefilm materials exist with relative dielectric constant k, in the range2.5<k<3.5, few have lower permittivity. Among the materials with k<2.5are amorphous carbon alloys, fluorinated amorphous carbon alloys, andforms of porous silicon oxide.

[0004] The typical amorphous carbon alloy films have been shown to haveinadequate thermal stability, often decomposing at temperatures above200° C. It has also been shown that it is difficult to obtain goodadhesion between carbon alloys and the metal films used to form thecircuit interconnections. It is proposed that this problem can beovercome by the use of a reactive gas comprising a silane compoundhaving a strained silicon bond environment. The approach is to create acarbon based film with some minimal Si content. The presence of the Siallows the formation of a native Si—O siloxane or silicon oxide on thefilm surface, which improves adhesion compared to an all carbon surfaceas is found in a-C:H, and a-C:F:H and Teflon based films.

[0005] U.S. Pat. No. 6,440,876 to Wang et al. discloses the use of aSi—O—C in-ring cyclic siloxane precursor compound in the formation of afilm having a dielectric constant, k, of less than 2.5.

[0006] The use of silacyclobutanes in forming amorphous SiC films havebeen described in U.S. Pat. No. 5,011,706 to Tarhay et al. This patentdiscloses a method of forming a continuous coating of amorphous siliconcarbide on the surface of articles by plasma enhanced chemical vapordeposition. The chemical vapor comprises a silicon containingcyclobutane.

[0007] It is an object of this invention to provide a method forproducing low dielectric permittivity films of hydrogenated siliconoxycarbide by plasma assisted polymerization of a cyclic silane compoundcontaining at least one strained silicon bond.

SUMMARY OF THE INVENTION

[0008] This invention pertains to a method of producing thin films ofhydrogenated silicon oxycarbide (H:SiOC) having low dielectricpermittivity on substrates, preferably semiconductor devices. The methodcomprises the plasma-assisted polymerization of a reactive gas mixturecomprising a cyclic silane compound containing at least one strainedsilicon bond (“cyclic silane compound”) and an oxygen providing gas.These films have a low dielectric constant and are particularly suitedas interlayer dielectrics.

DETAILED DESCRIPTION OF THE INVENTION

[0009] This invention pertains to a method for producing hydrogenatedsilicon oxycarbide films on substrate. Typical substrates include butare not limited to, semiconductor substrates, liquid crystal devices, alight emitting diode display device, and an organic light emittingdisplay device. The method for producing the films comprises the plasmaassisted polymerization of a reactive gas mixture comprising a cyclicsilane compound having at least one strained silicon bond (“cyclicsilane compound”) and an oxygen providing gas.

[0010] By “semiconductor substrate” it is meant to include, but not belimited to, silicon based devices and gallium arsenide based devicesintended for use in the manufacture of a semiconductor componentsincluding focal plane arrays, opto-electronic devices, photovoltaiccells, optical devices, transistor-like devices, 3-D devices,silicon-on-insulator devices, super lattice devices and the like. Thesemiconductor substrates may contain one or more layers of wiring. Thesemiconductor substrate may also be those substrates prior to theformation of any wiring layers.

[0011] Cyclic silane compounds are those compounds where one or moresilicon atoms are contained within at least one ring structure that doesnot include an oxygen atom in the ring structure. Such compounds musthave at least one ring and each ring must have a minimum of threesubstituent atoms wherein at least one of the substituent atoms are Siand each ring must not contain an oxygen atom. Examples of cyclic silanecompounds include silicon-containing cyclobutanes, silicon-containingcyclopentanes, silicon-containing cyclohexanes,sila-5-spiro[4,4]nona-2,7-diene, bi-cyclic compounds and relatedmaterials.

[0012] Silicon-containing cyclobutanes with one silicon atom includecompounds represented by the formula

[0013] where each R is independently selected from the group consistingof hydrogen, fluorine, and hydrocarbon radicals having 1 or more carbonatoms and each R′ is independently selected from the group consisting ofhydrogen and hydrocarbon radicals having 1 or more carbon atoms.Typically any hydrocarbon radicals will have 1 to 4 carbon atoms. Forexample, useful silicon-containing cyclobutanes include the parentcompound silacyclobutane (H₂SiC₃H₆) and derivatives such as1,1-difluorosilacyclobutane, 1-methylsilacyclobutane,1,1-dimethylsilacyclobutane, 1,1-ethylmethylsilacyclobutane,1-butylsilacyclobutane, 2,4-dimethylsilacyclobutane,3,3-diethylsilacyclobutane, and 3,3-ethylpropylsilacyclobutane.

[0014] Silicon-containing cyclobutanes with two silicon atoms includecompounds represented by the formula

[0015] where each R and R′ has the same meaning as described previously.For example, useful silicon-containing cyclobutanes include the parentcompound 1,3-disilacyclobutane and derivatives such as1,1,3,3-tetrafluoro-1,3-disilacyclobutane,1-methyl-1,3-disilacyclobutane, 1,3-dimethyl-1,3-disilacyclobutane,1,1-ethylmethyl-1,3-disilacyclobutane, 1-butyl-1,3-disilacyclobutane,2,4-dimethyl-1,3-disilacyclobutane, 2,2-diethyl-1,3-disilacyclobutane,and 2,4-ethylpropyl-1,3-disilacyclobutane.

[0016] The above silacyclobutane and 1,3-disilacyclobutane as well astheir derivatives are known materials and methods for their productionare known in the art. For example, the preparation of silacyclobutanefrom 1,1-dichlorosilacyclobutane by lithium aluminum hydride reductionis described by J. Laane, J. Am. Chem. Soc. 89, 1144 (1967).

[0017] Other cyclic silane compounds include

[0018] The reactive gas mixture used to produce the H:SiOC films alsocomprises a controlled amount of an oxygen providing gas. The oxygen maybe controlled by the type of oxygen providing gas used, or by the amountof oxygen providing gas that is used. If too much oxygen is present inthe deposition chamber a silicon oxide film with a stoichiometry closeto SiO₂ will be produced and the dielectric constant will be higher thandesired. If too little oxygen is present in the deposition chamber asilicon carbide film with a stoichiometry close to SiC:H will beproduced.

[0019] Oxygen providing gases include, but are not limited to oxygen,air, nitrous oxide, nitric oxide, carbon monoxide, carbon dioxide,peroxides, and sulfur dioxide (SO₂), typically nitrous oxide. The amountof oxygen providing gas is typically 0.1 to 10 volume parts oxygenproviding gas per volume part of cyclic silane compound, alternativelyfrom 0.2 to 7 volume parts of oxygen providing gas per volume part ofcyclic silane compound. One skilled in the art will be able to readilydetermine the amount of oxygen providing gas based on the type of oxygenproviding gas and the deposition conditions.

[0020] Other materials may be present in the reactive gas mixture. Forexample, carrier gases such as helium or argon, dopants such asphosphine or diborane, halogens such as fluorine, halogen-containinggases such as SiF₄, CF₄, C₃F₆ and C₄F₈ or any other material thatprovides additional desirable properties to the film may be present.

[0021] The reactive gas mixture is introduced into a deposition chambercontaining a substrate, preferably a semiconductor substrate, whereinthe polymerization of the cyclic silane compound is induced resulting inthe deposition of a film on the substrate wherein the film compriseshydrogen, silicon, carbon and oxygen and has a low dielectric constant(>2.0 to <3.2). Plasma enhanced chemical vapor deposition (PECVD) ispreferred due to the low temperatures that can be used and wide use inthe industry.

[0022] In PECVD the gas mixture is reacted by passing it through aplasma field. The plasmas used in such processes comprise energy derivedfrom a variety of sources such as electric discharges, electromagneticfields in the radio frequency or microwave range, lasers or particlebeams. Generally preferred in the plasma deposition processes is the useof radio frequency (10 kHz to 10² MHz) or microwave (1.0 to 10 GHz)energy at moderate power densities (0.1 to 5 watts/cm²). The specificfrequency, power and pressure, however are generally tailored to theequipment. Preferably the films are produced using PECVD at a power of20 to 1000 W; a pressure of 1 to 10,000 mTorr; and a temperature of 25to 500° C. Confined, low pressure (1-5 mTorr) microwave frequencyplasmas, often referred to as high density plasmas, can be combined witha RF frequency excitation in a process which helps planarize a varyingsurface topography during CVD growth. This process is useful in theformation of interlayer dielectrics.

[0023] The hydrogenated silicon oxycarbide films produced herein may berepresented by the general formula Si_(w)O_(x)C_(y)H_(z) wherein theratio of C:Si can be in the range of about 1:1 to about 10:1 and theratio of O:Si can be in the range of about 0.1:1 to about 1.5:1 with thebalance being hydrogen. The C:Si ratio is typically determined by theC:Si ratio of the cyclic silane compound.

[0024] The films produced herein may be of varying thicknesses. Filmshaving thicknesses of 0.01 to 10 μm may be produced by the method ofthis invention. Alternatively, the films have a thickness of 0.5 to 3.0μm.

[0025] An advantage to the method of this invention is the ability tolink successive growth processes to produce multilayer structures ofSiO₂, H:SiOC and/or SiC:H for example SiO₂/H:SiOC/SiO₂ orSiC:H/H:SiOC/SiC:H, by increasing or deleting the oxygen providing gasat the appropriate time during the CVD process. It is preferred toproduce discreet layers by stopping the reactive gas flow, adjusting theamount of oxygen providing gas and thereafter resuming the reactive gasflow to produce the next layer.

[0026] The films produced herein, due to the low dielectric constant,are particularly suited as interlayer dielectrics in semiconductorintegrated circuit manufacturing including, but not limited to, gatedielectrics, premetal and intermetal dielectrics and passivationcoatings. The films produced herein have a dielectric constant, k, of≧2.0 to ≦3.2, alternatively ≧2.2 to ≦2.8.

[0027] The following non-limiting examples re provided so that oneskilled in the art may more readily understand the invention.

EXAMPLES Example 1

[0028] A reactive gas mixture comprising dimethylsilacyclobutane (DMSCB)and nitrous oxide, N₂O, (See Tables 1 for gas flow amounts) wasintroduced into a capacitively coupled parallel plate PECVD system at adeposition temperature was 350° C. The power, pressure conditions thatthe PECVD system was operated under are given in Table 1. Helium wasused as a carrier gas in runs 1-1,1-14, and 1-15. The films were formedon Si(100) wafers as the substrate. The refractive index (RI) wasmeasure on as-deposited films. The dielectric constant (k) was measuredafter the films were annealed for one hour in N₂ ambient and 400° C.following metal deposition. The process conditions and results are inTable 1. TABLE 1 Examples of DMSCB based a-SiCO:H films. Dep temp = 350°C. Dep Press, Power, DMSCB N₂O He Rate Post-anneal K* Run ID (torr)(watt) (sccm) (sccm) (sccm) (Å/min) RI Kavg* STD 1-1 3 300 150 125 753239 1.4 2.528 0.0283 1-2 3 300 100 50 1878 1.5021 2.651 0.0988 1-3 3400 100 50 3665 1.4661 2.677 0.0920 1-4 3 300 115 50 1777 1.4955 2.6020.1161 1-5 3 300 85 50 1929 1.4991 2.740 0.0110 1-6 3 250 100 50 14681.5036 2.593 0.2057 1-7 3.8 300 100 50 1803 1.5035 2.683 0.0390 1-8 2300 100 700 7608 1.4333 2.604 0.2420 1-9 3 300 130 50 1626 1.4978 2.5450.0632 1-10 3 400 130 50 2375 1.5155 2.650 0.0330 1-11 3 300 100 7007482 1.4186 2.838 0.0546 1-12 1 300 100 50 1110 1.4087 2.793 0.1935 1-131 400 100 50 844 1.5154 3.041 0.1039 1-14 5 400 50 350 100 4943 1.37413.101 0.0750 1-15 5 400 100 50 100 2692 1.5218 2.583 0.1234

EXAMPLE 2 (COMPARATIVE)

[0029] a-SiC:H films were produced using DMSCB as described in Example 1except that nitrous oxide (N₂O) was not used in the reactive gasmixture. TABLE 2 Examples of DMSCB a-SiC:H films. Dep temp = 350° C.Press, Power, DMSCB He Dep Rate Post annealed K* Run ID (torr) (watt)(sccm) (sccm) (Å/min) RI Kavg STD C2-1 3 200 150 200 140 1.7106 4.3500.1633 C2-2 3 400 150 200 273 1.7375 4.271 0.1612 C2-3 5 300 50 80 2871.6146 3.919 0.0239 C2-4 5 200 50 80 125 1.6172 4.044 0.1137 C2-5 2 40050 80 580 1.7749 4.357 0.0458 C2-6 2 300 50 80 376 1.783 4.474 0.1114

EXAMPLE 3

[0030] Films produced in Run 1-15 of Example 1 and Run C₂₋₄ of Example 2were analyzed for composition using Rutherford Back Scattering-HydrogenForward Scattering (Ion Scattering Spectrometry). The results of thisanalysis are given in Table 3. As can be seen by these results. Theleakage current density was also measured on both films. For thea-SiCO:H film the leakage current density at 1 MV/cm was less than 10⁻¹⁰Å/cm². For the a-SiC:H film the leakage current density at 1 MV/cm wasless than 10⁻¹⁰ Å/cm².

[0031] As can be seen by these results it is possible to produce filmshaving low leakage current density with increased C:Si ratios.

[0032] For additional comparison, a-SiCO:H and a-SiC:H films wereproduced using trimethylsilane (TMS). TABLE 3 Composition of DMSCB baseda-SiCO:H and a-SiCO:H films Atom LKG Vbd density Density (Å/cm² @ (mv/cm@ Process Si N H O C (atoms/cm²) (g/cm³) O/Si C/Si 1 MV/cm) 1 mA/cm²)DMSCB 0.11 0 0.46 0.1 0.33 1.78E+18 1.15 0.91 3 7.67 × 10⁻¹¹ >4 a-SiCO:HDMSCB 0.16 0 0.4 0.08 0.36 4.09E+17 1.12 0.5 2.25 2.39 × 10⁻¹¹ >4a-SiC:H TMS 0.15 0.02 0.36 0.15 0.32 6.55E+22 1.17 1.00 2.14   3 ×10⁻¹⁰* >4 a-SiCO:H TMS 0.30 0 0.14 0.05 0.48 7.47E+22 1.85 0.17 1.6 5.33× 10⁻⁹ 2.5 a-SiC:H

What is claimed is:
 1. A chemical vapor deposition method for producinghydrogenated silicon oxycarbide films comprising introducing a reactivegas mixture comprising (i) a cyclic silane compound containing at leastone strained silicon bond and (ii) an oxygen providing gas into adeposition chamber containing a substrate and inducing a reactionbetween the cyclic silane compound and oxygen providing gas at atemperature of 25° C. to 500° C.; wherein there is a controlled amountof oxygen present during the reaction to provide a film on the substratecomprising hydrogen, silicon, carbon and oxygen having a dielectricconstant in the range of 2.0 to 3.2.
 2. The method as claimed in claim 1wherein the cyclic silane compound is selected from the group consistingof silicon-containing cyclobutanes, silicon-containing cyclopentanes,silicon-containing cyclohexanes, sila-5-spiro[4,4]nona-2,7-diene, andbi-cyclic compounds.
 3. The method as claimed in claim 1 wherein thecyclic silane compound is selected from

where each R is independently selected from the group consisting ofhydrogen, fluorine, and hydrocarbon radicals having at least 1 carbonatom and each R′ is independently selected from the group consisting ofhydrogen and hydrocarbon radicals having at least one carbon atom. 4.The method as claimed in claim 2 wherein the cyclic silane compound is asilicon-containing cyclobutane.
 5. The method as claimed in claim 4wherein the silicon-containing cyclobutane has the formula

where each R is independently selected from the group consisting ofhydrogen, fluorine, and hydrocarbon radicals having at least 1 carbonatom and each R′ is independently selected from the group consisting ofhydrogen and hydrocarbon radicals having at least 1 carbon atom.
 6. Themethod as claimed in claim 4 wherein the silicon-containing cyclobutanehas the formula

where each R is independently selected from the group consisting ofhydrogen, fluorine, and hydrocarbon radicals having at least one 1carbon atom and each R′ is independently selected from the groupconsisting of hydrogen and hydrocarbon radicals having at least 1 carbonatom.
 7. The method as claimed in claim 1 wherein the oxygen providinggas is selected from the group consisting of oxygen, air, peroxides,sulfur dioxide, carbon monoxide, carbon dioxide, nitrous oxide andnitric oxide.
 8. The method as claimed in claim 1 wherein the oxygenproviding gas is nitrous oxide.
 9. The method as claimed in claim 1wherein the cyclic silane compound is dimethylsilacyclobutane and theoxygen providing gas is nitrous oxide.
 10. The method as claimed inclaim 1 wherein the amount of oxygen providing gas is in the range of0.1 to less than 10 volume parts oxygen providing gas per volume part ofcyclic silane compound.
 11. The method as claimed in claim 1 wherein theamount of oxygen providing gas is 0.2 to 7 volume parts of oxygenproviding gas per volume part of cyclic silane compound.
 12. The methodas claimed in claim 1 wherein the reaction is induced by exposing thereactive gas mixture to plasma.
 13. The method as claimed in claim 12wherein the reaction is induced by exposing the reactive gas mixture toplasma at a power of 20 to 1000 W, a pressure of 1 to 10,000 mTorr, anda temperature of 25 to 500° C.
 14. The method as claimed in claim 1wherein the film has a dielectric constant in the range of 2.2 to 2.8.15. The method as claimed in claim 1 wherein the film has a dielectricconstant in the range of 2.5 to 2.8.
 16. The method as claimed in claim1 wherein the reactive gas mixture additionally comprises a carrier gas.17. The method as claimed in claim 1 wherein the hydrogenated siliconoxycarbide film has a thickness of 0.01 to 10 μm.
 18. The method asclaimed in claim 1 wherein the hydrogenated silicon oxycarbide film hasa thickness of 0.5 to 3.0 μm.
 19. The method as claimed in claim 1wherein the substrate is a semiconductor substrate.
 20. The method asclaimed in claim 1 wherein the substrate is selected from a liquidcrystal device, a light emitting diode display device and an organiclight emitting diode display device.
 21. The method as claimed in claim1 wherein the amount of oxygen providing gas is increased or decreasedduring the reaction between the cyclic silane compound and the oxygenproviding gas to produce a film containing successive layers selectedfrom the group consisting of SiO₂, H:SiOC and SiC:H.
 22. The method asclaimed in claim 1 wherein the reaction is induced by exposing thereactive gas mixture to confined, low-pressure microwave frequencyplasma combined with RF frequency excitation.
 23. A semiconductor devicehaving thereon a film produced by the method as claimed in claim 1.